Injection needle

ABSTRACT

An injection needle ( 1 ), comprising a needle tip ( 5 ) provided by forming at least two or more ground surfaces ( 3   b,    3   c ) after a first ground surface ( 3   a ) is formed at the tip of a needle tube ( 2 ), characterized in that the needle tip ( 5 ) is not present on a central plane ( 6 ), where a plane vertically crossing the first ground surface ( 3   a ) and including the center axis ( 8 ) of the needle tube ( 2 ) is the central plane ( 6 ), whereby the injection needle can reduce boring pain provided to a patient when the needle is pierced into a skin.

TECHNICAL FIELD

The present invention relates to an injection needle for medical use,and more particularly to an. injection needle having a small diameterfor use in self-injection.

BACKGROUND ART

Injection needles for medical use generally have an edge surface withtwo slant angles as viewed in side elevation, which is generally calleda lancet point. FIG. 7 is a plan view of the edge surface of a lancetpoint structure of a conventional injection needle. In FIG. 7, it isassumed that the injection needle has a needle point at a distal endthereof and an opposite end at a proximal end thereof. The injectionneedle 11 has a needle tube 12 including an edge surface 13 disposed onthe distal end. The edge surface 13 includes a first ground facet 13 aformed closer to the proximal end, and a second ground facet 13 b and athird ground facet 13 c that are formed closer to the distal end thanthe first ground facet 13 a. The second ground facet 13 b and the thirdground facet 13 c are symmetrical in shape with respect to the majoraxis of the edge surface that is of a substantially elliptical shape.The sharp needle point 15 on the distal end of the edge surface 13 ispresent on a central plane 16 that crosses the first ground facet 13 aperpendicularly and includes the central axis of the needle tube 12.

FIGS. 8(a) through 8(c) are views illustrative of a process of formingthe edge surface 13 of the lancet point structure, and show in sideelevation the injection needle 11 in the vicinity of its distal endillustrated in FIG. 7. For forming the edge surface 13 of the lancetpoint structure, as shown in FIG. 8(a), a grinding wheel is applied tothe distal end portion of the needle tube 12, which is in the form of ahollow tube, at an angle α (0 °<α<90°) with respect to the central axis18 of the needle tube 12, and grinds the distal end portion to form thefirst ground facet 13 a whose angle with respect to the central axis 18of the needle tube 12 is α.

Then, as shown in FIG. 8(b), the needle tube 12 is turned a certainangle about the central axis 18 toward the viewer of FIG. 8(b). Thegrinding wheel is applied to the distal end portion of the needle tube12 at an angle φ (0°<α<φ<90°) with respect to the first ground facet 13a around the central axis 18 of the needle tube 12, and grinds thedistal end portion to form the second ground facet 13 b whose angle withrespect to the central axis 18 of the needle tube 12 is φ.

Thereafter, as shown in FIG. 8(c), the needle tube 12 is turned aboutthe central axis 18 from the state shown in FIG. 8(a) away from theviewer of FIG. 8(b). The grinding wheel is applied to the distal endportion of the needle tube 12 at an angle θ (0°<α<θ=φ<90°), which isequal to the angle φ, with respect to the first ground facet 13 a aroundthe central axis 18 of the needle tube 12, and grinds the distal endportion to form the third ground facet 13 c whose angle with respect tothe central axis 18 of the needle tube 12 is θ (=φ). The angle throughwhich the needle tube 12 is turned toward the viewer of FIG. 8(b) isequal to the angle through which the needle tube 12 is turned toward theviewer of FIG. 8(c). In this manner, as shown in FIG. 7, the secondground facet 13 b and the third ground facet 13 c are symmetrical inshape with respect to the major axis of the edge surface which is of asubstantially elliptical shape.

The injection needle 11 having the edge surface 13 of the conventionallancet point structure can easily pierce a skin 7 as the force requiredto penetrate the skin 7 is small, and poses a reduced burden on thepatient. However, inasmuch as the edge surface 13 is of a symmetricalshape, when the needle 11 pierces the skin, or more specifically, whenthe injection needle 11 pierces a skin 7 perpendicularly thereto forinsulin injection by way of self-injection, the sharp needle point 15 onthe distal end of the edge surface 13 first makes point-to-point contactwith the skin 7, often causing sharp pain. The puncture pain issustained until the edge surface 13 goes fully through the skin 7. Inthe present specification, the pain caused when the distal end of theedge surface 13 contacts the skin 7 and the edge surface 13 is furtherforced into the skin 7 is referred to as “puncture pain”.

In view of the above conventional problems, it is therefore an object ofthe present invention to provide an injection needle which is capable ofreducing puncture pain caused when the injection needle penetrates theskin.

DISCLOSURE OF INVENTION

The above object can be accomplished by the present invention asfollows:

-   -   (1) According to the present invention, an injection needle        having a first ground facet formed on a distal end of a needle        tube and at least two ground facets subsequently formed to        provide a needle point is characterized in that    -   a plane which crosses the first ground facet perpendicularly        thereto and includes a central axis of the needle tube is        regarded as a central plane, and the needle point is not present        on the central plane.    -   (2) According to the present invention, in the injection needle        described above in (1), the minimum distance between the needle        point and the central plane is in the range from 3 to 20% of the        maximum outside diameter of the first ground facet in the        direction of a minor axis thereof.    -   (3) According to the present invention, in the injection needle        described above in (1), the minimum distance between the needle        point and the central plane is in the range from 8 to 100 μm.    -   (4) According to the present invention, an injection needle        having an edge surface including three ground facets formed on a        distal end of a needle tube to provide a needle point is        characterized in that    -   one of the ground facets which is remotest from the needle point        is regarded as a first ground facet, and the other ground facets        as a second ground facet and a third ground facet; and    -   an angle α between the first ground facet and a central axis of        the needle point, an angle φ between the second ground facet and        the central axis of the needle point, and an angle θ between the        third ground facet and the central axis of the needle point are        related to each other by: α<φ,α<θ, and φ≠θ.    -   (5) According to the present invention, in the injection needle        described above in (4), a plane which crosses the first ground        facet perpendicularly thereto and includes the central axis of        the needle tube is regarded as a central plane; and    -   the minimum distance between the needle point and the central        plane is in the range from 3 to 20% of the maximum outside        diameter of the edge surface in the direction of a minor axis        thereof.    -   (6) According to the present invention, in the injection needle        described above in (4), the minimum distance between the needle        point and the central plane is in the range from 8 to 100 μm.    -   (7) According to the present invention, in the injection needle        described above in (4) through (6), the length of the second        ground facet in the direction of the central axis and the length        of the third ground facet in the direction of the central axis        are in the range from 20 to 80% of the whole length of the        ground facets in the direction of the central axis.    -   (8) According to the present invention, in the injection needle        described above in (1) through (7), when the injection needle        pierces a silicone rubber sheet having a thickness of 0.5 mm at        a penetration speed of 10 mm/min., an initial value of the load        with respect to a penetration distance is 6 gf/mm or less.

The injection needle according to the present invention is capable ofeffectively distributing forces that are applied from the edge surfaceto the skin when the edge surface is brought into contact with the skinfrom its distal end and further forced into the skin. Therefore, thepuncture pain that is caused when the injection needle pierces the skincan be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view showing an edge surface portion of an injectionneedle according to an embodiment of the present invention;

FIGS. 2(a) through 2(c) are side elevational views of the injectionneedle in the vicinity of its distal end illustrated in FIG. 1, FIG.2(a) being a side elevational view of the injection needle with a firstground facet 3 a being viewed flush with line of sight, FIG. 2(b) beinga side elevational view of the injection needle with a second groundfacet 3 b being viewed flush with line of sight, FIG. 2(c) being a sideelevational view of the injection needle with a third ground facet 3 cbeing viewed flush with line of sight, and FIG. 2(d) being across-sectional view taken along line A-A′ of FIG. 2(a);

FIG. 3(a) is a plan view of an edge surface portion of an injectionneedle according to Inventive Example 1, FIG. 3(b) is a left sideelevational view of the injection needle 1 in the vicinity of its distalend illustrated in FIG. 3(a), and FIG. 3(c) is a right side elevationalview of the injection needle 1 in the vicinity of its distal endillustrated in FIG. 3(a), FIGS. 3(b) and 3(c) being views of theinjection needle with a first ground facet 3a being viewed flush withline of sight;

FIG. 4(a) is a plan view of an edge surface portion of an injectionneedle according to Inventive Example 2, FIG. 4(b) is a left sideelevational view of the injection needle 1 in the vicinity of its distalend illustrated in FIG. 4(a), and FIG. 4(c) is a right side elevationalview of the injection needle 1 in the vicinity of its distal endillustrated in FIG. 4(a), FIGS. 4(b) and 4(c) being views of theinjection needle with a first ground facet 3 a being viewed flush withline of sight;

FIG. 5(a) is a plan view of an edge surface portion of an injectionneedle according to Inventive Example 3, FIG. 5(b) is a left sideelevational view of the injection needle 1 in the vicinity of its distalend illustrated in FIG. 5(a), and FIG. 5(c) is a right side elevationalview of the injection needle 1 in the vicinity of its distal endillustrated in FIG. 5(a), FIGS. 5(b) and 5(c) being views of theinjection needle with a first ground facet 3 a being viewed flush withline of sight;

FIG. 6 is a graph showing penetration resistance curves measured inExamples;

FIG. 7 is a plan view of an edge surface portion of a conventionalinjection needle;

FIGS. 8(a) through 8(c) are side elevational views of the injectionneedle 11 in the vicinity of its distal end illustrated in FIG. 7, FIG.8(a) being a side elevational view of the injection needle with a firstground facet 13 a being viewed flush with line of sight, FIG. 8(b) beinga side elevational view of the injection needle with a second groundfacet 13 b being viewed flush with line of sight, FIG. 8(c) being a sideelevational view of the injection needle with a third ground facet 13 cbeing viewed flush with line of sight, and FIG. 8(d) being across-sectional view taken along line B-B′ of FIG. 8(a).

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a plan view showing an edge surface portion of an injectionneedle according to an embodiment of the present invention. In FIG. 1,it is assumed that the injection needle has a needle point at a distalend thereof and an opposite end at a proximal end thereof. The injectionneedle 1 according to the present invention has a needle tube 2including an edge surface 3 disposed on the distal end. The edge surface3 includes a first ground facet 3 a positioned closer to the proximalend and remotest from a needle point 5, and two ground facets, i.e., asecond ground facet 3 b and a third ground facet 3 c, positioned closerto the distal end than the first ground facet 3 a. Thus, the injectionneedle 1 according to the present invention has the edge surface 3 thatis of a structure similar to an edge surface of the conventional lancetpoint structure. Therefore, the edge surface 3 can be formed in the samemanner as an edge surface of the conventional lancet point structure.Specifically, the distal end portion of the needle tube 2 is ground at acertain angle a with respect to the central axis 8 of the needle tube 2,forming the first ground facet 3 a. Then, the needle tube 2 is turnedabout the central axis 8 through angles, and the first ground facet 3 a,which is of a substantially elliptical shape, is ground on differentsides of the major axis thereof at angles φ, θ greater than the angle α,forming the second ground facet 3 b and the third ground facet 3 c. Theinjection needle 1 according to the present invention is formed suchthat the needle point 5 is not present on a central plane 6 that crossesthe first ground facet 3 a perpendicularly and includes the central axisof the needle tube 2. Stated otherwise, the injection needle 1 accordingto the present invention is formed such that the needle point 5positioned on the distal end of the edge surface 3 is not present on themajor axis of the substantially elliptical shape of the first groundfacet 3 a when it is first formed.

The injection needle 1 according to the present invention ischaracterized in that the needle point 5 is not present on the centralplane 6 that crosses the first ground facet 3 a perpendicularly andincludes the central axis of the needle tube 2 (also referred to simplyas “central plane 6”). Of edges 4 b, 4 c provided by the second groundfacet 3 b and the third ground facet 3 c, either one (in FIG. 1, theedge 4 c provided by the third ground facet 3 c) projects toward thedistal end of the edge surface 3. Since the injection needle 1 accordingto the present invention has its edge surface 3 thus constructed, whenthe injection needle 1 pierces a skin 7, the injection needle 1 firstcontacts the skin 7 not by way of point-to-point contact between theskin 7 and the sharp needle point 5, but by way of more linear contactbetween the skin 7 and a needle region including the needle point 5 anda portion of the curved edge 4 b or 4 c projecting toward the distal endof the edge surface 3 (a contact portion has a linear shape).Accordingly, when the distal end of the edge surface 3 contacts the skin7 and the edge surface 3 is further forced into the skin 7, forces thatare applied from the edge surface 3 to the skin 7 are distributed. As aresult, the puncture pain caused when the injection needle 1 penetratesthe skin 7 can be reduced.

The injection needle 1 according to the present invention may bearranged such that when the injection needle 1 penetrates the skin 7,the needle point 5 may not make initial contact with the skin 7, butonly the portion of the curved edge 4 b or 4 c projecting toward thedistal end of the edge surface 3 may contact the skin 7 such that acontact portion has a linear shape. In this case, the puncture paincaused when the injection needle 1 penetrates the skin 7 can also bereduced. The direction in which the edge 4 b or 4 c projects is notlimited in particular, but may be the direction of the second groundfacet 3 b, i.e., the edge 4 b may project. That is, the needle point 5may be positioned on either side of the central plane 6.

With the injection needle 1 according to the present invention, sincethe needle point 5 is not on the central plane 6 as shown in FIG. 1, theneedle point 5 is spaced a distance from the central plane 6. Theminimum distance S between the needle point 5 and the central plane 6should preferably be in the range of 3 to 20% of the maximum outsidediameter of the first ground facet 3 a in the direction of the minoraxis of the substantially elliptical shape of the first ground facet 3 athat is initially formed, and more preferably in the range of 5 to 15%of the maximum outside diameter. As described later on, since theinjection needle 1 according to the present invention should preferablybe used as an injection needle having a small diameter for use ininsulin injection and self-injection, with the outside diameter of 0.36mm or less, the minimum distance between the needle point 5 and thecentral plane 6 should preferably be in the range from 8 to 100 μm andmore preferably in the range from 8 to 35 μm.

With the minimum distance S between the needle point 5 and the centralplane 6 being in the above range, since the portion of the edge surface3 which makes initial contact with the skin 7 is of a more linear shape,when the edge surface 3 is brought into contact with the skin 7 from thedistal end thereof and forced into the skin 7, forces that are appliedfrom the edge surface 3 to the skin 7 are sufficiently distributed, thusreducing the puncture pain. With the minimum distance S between theneedle point 5 and the central plane 6 being in the above range,furthermore, the portions of the edges 4 b, 4 c which project toward thedistal end of the edge surface 3 and will make initial contact with theskin 7 are not too large, so that when the edge surface 3 is furtherforced into the skin 7, the penetration of the skin by the edge surface3 is not obstructed, and the puncture pain is not increased.

The injection needle according to the present invention will further bedescribed with reference to FIG. 2. FIGS. 2(a) through 2(c) are sideelevational views of the injection needle 1 in the vicinity of itsdistal end illustrated in FIG. 1. FIG. 2(a) is a side elevational viewof the injection needle with a first ground facet 3 a being viewed flushwith line of sight, FIG. 2(b) is a side elevational view of theinjection needle with a second ground facet 3 b being viewed flush withline of sight, and FIG. 2(c) is a side elevational view of the injectionneedle with a third ground facet 3 c being viewed flush with line ofsight. FIG. 2(d) is a cross-sectional view taken along line A-A′ of FIG.2(a). In FIG. 2(d), the angle γ is an angle formed between the secondground facet 3 b and the third ground facet 3 c in a cross section thatis perpendicular to the central axis 8 of the injection needle 1.

As shown in FIG. 2(a), the first ground facet 3 a has an angle α withrespect to the central axis 8 of the needle tube 2. As shown in FIG.2(b), the second ground facet 3 b has an angle φ with respect to thecentral axis 8 of the needle tube 2. As shown in FIG. 2(c), the thirdground facet 3 c has an angle θ with respect to the central axis 8 ofthe needle tube 2. On the injection needle 1 according to the presentinvention, these angles α, φ, and θ have the following relationship:0°<α<φ≠θ<90°

The angle of the second ground facet 3 b (φ) and the third ground facet3 c (θ) with respect to the central axis 8 of the needle tube 2 isgreater than the angle of the first ground facet 3 a (α) similarly tothe edge surface of the conventional lancet point structure. Theinjection needle 1 according to the present invention is characterizedin that the angle φ and the angle θ are different from each other. Asdescribed above, with the injection needle 1 according to the presentinvention, after the first ground facet 3 a having the angle α withrespect to the central axis 8 of the needle tube 2 is formed on thedistal end portion of the needle tube 2, the second ground facet 3 b andthe third ground facet 3 c are formed on the different sides of themajor axis of the first ground facet 3 a which is of a substantiallyelliptical shape, respectively at the angle φ and the angle θ withrespect to the central axis 8 of the needle tube 2. Therefore, if theangle φ and the angle θ are different from each other, then either one(the third ground facet 3 c in FIG. 1) of the second ground facet 3 band the third ground facet 3 c is formed so as to project beyond thecentral plane 6 toward the other ground facet. Consequently, either one(4 c in FIG. 1) of the edges 4 b, 4 c provided by the second groundfacet 3 b and the third ground facet 3 c is of a shape projecting towardthe distal end of the edge surface 3. As described above, when theinjection needle 1 pierces the skin 7, the injection needle 1 firstcontacts the skin 7 not by way of point-to-point contact between theskin 7 and the sharp needle point 5, but by way of more linear contactbetween the skin 7 and a needle region including the needle point 5 anda portion of the curved edge 4 b or 4 c projecting toward the distal endof the edge surface 3, or more linear contact between the skin 7 and aportion of the curved edge 4 b or 4 c projecting toward the distal endof the edge surface 3 (that is, a contact portion has a linear shape).Accordingly, when the distal end of the edge surface 3 contacts the skin7 and the edge surface 3 is further forced into the skin 7, forces thatare applied from the edge surface 3 to the skin 7 are sufficientlydistributed, reducing the puncture pain.

With the injection needle 1 according to the present invention, as thesecond ground facet 3 b and the third ground facet 3 c is formed at thedifferent angles φ, θ with respect to the central axis 8 of the needletube 2, the second ground facet 3 b and the third ground facet 3 c havedifferent sizes and shapes, and the length C1 of the second ground facet3 b and the length C2 of the third ground facet 3 c in the direction ofthe central axis 8 of the needle tube 2 are different from each other,as shown in FIG. 1. C1 and C2 vary depending on the selection of theangles α, φ, and θ. With the injection needle 1 according to the presentinvention, it is preferable to set C1 and C2 to 20 through 80% of thelength A of the entire edge surface 3 along the central axis 8. If C1and C2 is in the above range, then the edges 4 b, 4 c provided by thesecond ground facet 3 b and the third ground facet 3 c have sizes largeenough to cut the skin 7, allowing the injection needle 1 to penetratethe skin 7 easily. Since no sharp protrusion is formed inside a jaw 9,when the portion of the injection needle 1 near the jaw 9 goes throughthe skin 7, the patient is prevented from feeling a strong pain.

With the injection needle 1 according to the present invention, sincethe needle point 5 is not on the central plane 6, when the injectionneedle 1 pierces the skin 7, the injection needle 1 first contacts theskin 7 not by way of point-to-point contact between the skin 7 and thesharp needle point 5, but by way of more linear contact between the skin7 and a needle region including the needle point 5 and a portion of thecurved edge 4 projecting toward the distal end of the edge surface 3 ormore linear contact between the skin 7 and a portion of the curved edge4 projecting toward the distal end of the edge surface 3 (that is, acontact portion has a linear shape). Therefore, when the edge surface 3is brought into contact with the skin 7 from its distal end and forcedinto the skin 7, forces that are applied from the edge surface 3 to theskin 7 are sufficiently distributed. Therefore, any increase in aninitial load on the object that is pierced by the injection needle 1according to the present invention is small. Specifically, when theinjection needle 1 according to the present invention pierces a siliconerubber sheet having a thickness of 0.5 mm at a penetration speed of 10mm/min., the initial value of the load with respect to the penetrationdistance should preferably be 6 gf/mm or less. Since the injectionneedle 1 according to the present invention should preferably be used asan injection needle for use in insulin injection and self-injection, theabove numerical value is measured when the injection needle pierces thesilicone rubber sheet perpendicularly thereto. This numerical valuediffers from silicone rubber to silicone rubber, but covers a wide rangeof silicone rubbers for medical use, e.g., for use in container plugsthat are to be pierced by injection needles for extracting or injectingcontents. In Examples to be described later, silicone rubber sheetshaving durometer hardness A50 (JIS-K6253) were used.

The injection needle 1 according to the present invention is similar tothe conventional injection needle except that the edge surface 3 has theabove structure. Therefore, the material and diameter of the needle tube2 may be selected in the range of the conventional injection needle. Theneedle tube 2 may be made of an iron material including stainless steel,a non-ferrous metal material such as aluminum, copper, titanium, or thelike, a heat-resistant material such as nickel, cobalt, or molybdenum, ametal having a low melting point such as lead or tin, a precious metalmaterial such as gold, silver, or platinum, or an alloy thereof.

Inasmuch as the injection needle 1 according to the present invention ispreferable as an injection needle for use in self-injection by thepatient, such as insulin injection, the injection needle 1 shouldpreferably have a small diameter. Specifically, the outside diameter ofthe needle tube 2 should preferably be 0.36 mm or less, or morepreferably in the range from 0.18 to 0.30 mm. The inside diameter of theneedle tube 2 should preferably be 0.19 mm or less, or more preferablyin the range from 0.07 to 0.17 mm.

As the injection needle for self-injection pierces the skinperpendicularly thereto, the distal end of the edge surface is broughtinto perpendicular contact with the skin. The conventional injectionneedle 11 having the sharp needle point 5 on the distal end of the edgesurface 13 as shown in FIG. 7 causes a sharp puncture pain when theinjection needle 11 pierces the skin 7 because the sharp needle point 5makes point-to-point contact with the skin 7 when the injection needle11 first contacts the skin 7. According to the present invention,however, as described above, the injection needle 1 first contacts theskin 7 by way of more linear contact between the skin 7 and a needleregion including the needle point 5 and a portion of the curved edge 4 bor 4 c projecting toward the distal end of the edge surface 3, or morelinear contact between the skin 7 and a portion of the curved edge 4 bor 4 c projecting toward the distal end of the edge surface 3 (that is,a contact portion has a linear shape). Accordingly, forces that areapplied from the edge surface 3 to the skin 7 are effectively reduced,and the injection needle 1 is highly effective to reduce the puncturepain caused when the injection needle 1 pierces the skin 7.

The needle tube 2 as seen in side elevation may be shaped not only as astraight tube, but also as a tapered shape whose outside diameterdecreases toward the distal end or the proximal end. The injectionneedle 1 having a tapered side-elevational shape may be either of atapered shape in its entirety or of a tapered shape in part of theneedle tube 2 or of a tapered shape in part of the edge surface 3. Theinjection needle 1 which is of a tapered shape in part of the edgesurface 3 may be produced by forming the second ground facet 3 b or thethird ground facet 3 c not in a single grinding process, but in aplurality of grinding processes performed at different angles withrespect to the central axis 8. Specifically, the needle point 5 of theinjection needle 1 according to the present invention may be produced byforming the first ground facet 3 a and thereafter forming three or moreground facets.

EXAMPLES

The distal end of a hollow tube (needle tube) of stainless steel havingan outside diameter of 0.2 mm and an inside diameter of 0.1 mm wasground according to the above procedure to produce an injection needleaccording to Inventive Example 1 having the edge surface 3 shown in FIG.3. The angles and dimensions of various regions of the injection needleaccording to Inventive Example 1 are shown in Table 1. In Table 1, γrepresents an angle formed between the second ground facet and the thirdground facet in a cross section that is perpendicular to the centralaxis of the injection needle, as shown in FIG. 2(d). Similarly, aninjection needle according to Inventive Example 2 having an edge surfaceshown in FIG. 4 and an injection needle according to Inventive Example 3having an edge surface shown in FIG. 5 were produced. ComparativeExamples 1 through 6 are conventional injection needles 11 of stainlesssteel, as shown in FIGS. 7 and 8, where the angle φ of the second groundfacet 13 b with respect to the central axis 18 of the needle tube 12 andthe angle θ of the third ground facet 13 c with respect to the centralaxis 18 of the needle tube 12 are equal to each other. In FIG. 7, thereference numeral 16 corresponds to the reference numeral 6 in FIG. 1.FIG. 8(d) is a cross-sectional view taken along line B-B′ of FIG. 8(a).In FIG. 8(d), the angle γ corresponds to the angle γ in FIG. 2(d). TABLE1 Edge surface shapes of injection needles according to InventiveExamples Inventive Example 1 2 3 Outside 0.2 0.2 0.2 diameter (mm) α(degrees) 8 8 8 γ (degrees) 136 130 130 φ (degrees) 12 14 18 θ (degrees)18 15 13 s (μm) 13 29 20 C1/A 0.58 0.47 0.28 C2/A 0.29 0.56 0.65

TABLE 2 Edge surface shapes of injection needles according toComparative Examples Inventive Example 1 2 3 4 5 6 Outside 0.2 0.2 0.250.25 0.3 0.3 diameter (mm) α (degrees) 9 8.5 9 9 9 9 γ (degrees) 130 129120 130 120 130 φ (degrees) 18 18 18 22 18 22 θ (degrees) 18 18 18 22 1822 s (μm) 0 0 0 0 0 0 C1/A 0.43 0.36 0.46 0.34 0.47 0.34 C2/A 0.43 0.360.46 0.34 0.47 0.34The injection needles according to Inventive Examples 1 through 3 andComparative Examples 1 through 6 were use to pierce a silicone rubbersheet (durometer hardness A50: JIS-K6253) having a thickness of 0.5 mm,and penetration resistance curves were measured using an autograph(manufactured by Shimadzu Corp. AGS-1kNG). The penetration speed was 10mm/min. The obtained penetration resistance curves are shown in FIG. 6.There has been no significant difference between the penetrationresistance curves of Inventive Example 3 and Inventive Example 1.

As can be seen from FIG. 6, the penetration resistance curves aredivided into a point M where the distal end (needle point) of the edgesurface makes initial contact with the object (silicone rubber sheet) tobe pierced, a point N where the needle point penetrates the objecthaving the thickness of 0.5 mm, a point O where the entire edge surfacepenetrates the object, and a point P where the needle tube passesthrough the object. The penetration resistance curves according to theInventive Examples indicate that the gradients of the penetrationresistance curves after the distal end (needle point) of the edgesurface makes initial contact with the object until the needle pointpenetrates the object, i.e., between the points M, N, are smaller thanthose of the Comparative Examples. The gradients of the penetrationresistance curves are shown in Table 3. TABLE 3 Gradients of penetrationresistance curves between the points M, N Specimen Gradient (gf/mm)Inventive Example 1 5.31 Inventive Example 2 5.13 Inventive Example 35.36 Comparative Example 1 9.76 Comparative Example 2 8.92 ComparativeExample 3 8.35 Comparative Example 4 8.12 Comparative Example 5 8.10Comparative Example 6 9.76

The measured penetration resistance curves show that the injectionneedles according to Inventive Examples 1 through 3 have smallergradients of penetration resistance curves between the points M, N thaninjection needles according to Comparative Examples 1 through 6. Thisindicates that when the edge surface is brought into contact with theobject from its distal end and further forced into the object, forcesthat are applied from the edge surface to the object are sufficientlydistributed. Therefore, as described above, the puncture pain causedwhen the injection needle penetrates the skin is reduced.

According to the Comparative Examples, penetration resistance curveswere measured using injection needle having different outside diameters,and exhibited substantially the same gradients. This indicates that thegradients of the penetration resistance curves do not depend upon thediameters of the injection needles. Since the injection needle accordingto the present invention has the edge surface of a particular structure,i.e., a structure in which the needle point is not present on thecentral plane, the gradient of the penetration resistance curve betweenthe points M, N is small. Therefore, when the edge surface is broughtinto contact with the object from its distal end and further forced intothe object, forces that are applied from the edge surface to the objectare sufficiently distributed.

Industrial Applicability

As described above, the injection needle according to the presentinvention is capable of effectively distributing forces that are appliedfrom the edge surface to the skin when the edge surface is brought intocontact with the skin from its distal end and further forced into theskin. Therefore, the puncture pain that is caused to the patient whenthe injection needle pierces the skin can be reduced, allowing thepatient to use the injection needle comfortably with ease.

1. An injection needle having a first ground facet formed on a distalend of a needle tube and at least two ground facets subsequently formedto provide a needle point, characterized in that a plane which crossessaid first ground facet perpendicularly thereto and comprises a centralaxis of said needle tube is regarded as a central plane; and the needlepoint is not present on said central plane.
 2. An injection needleaccording to claim 1, wherein the minimum distance between said needlepoint and said central plane is in the range from 3 to 20% of themaximum outside diameter of said first ground facet in the direction ofa minor axis thereof.
 3. An injection needle having an edge surfacecomprising three ground facets formed on a distal end of a needle tubeto provide a needle point, characterized in that one of the groundfacets which is remotest from said needle point is regarded as a firstground facet, and the other ground facets as a second ground facet and athird ground facet; and an angle α between said first ground facet and acentral axis of said needle point, an angle φ between said second groundfacet and the central axis of said needle point, and an angle θ betweensaid third ground facet and the central axis of said needle point arerelated to each other by: α<φ, α<θ, and φ≠θ.
 4. An injection needleaccording to claim 3, wherein a plane which crosses said first groundfacet perpendicularly thereto and comprises the central axis of saidneedle tube is regarded as a central plane; and the minimum distancebetween said needle point and said central plane is in the range from 3to 20% of the maximum outside diameter of said edge surface in thedirection of a minor axis thereof.
 5. An injection needle according toclaim 3, wherein the length of said second ground facet in the directionof the central axis and the length of said third ground facet in thedirection of the central axis are in the range from 20 to 80% of thewhole length of the ground facets in the direction of the central axis.6. An injection needle according to claim 1, wherein when the injectionneedle pierces a silicone rubber sheet having a thickness of 0.5 mm at apenetration speed of 10 mm/min., an initial value of the load withrespect to a penetration distance is 6 gf/mm or less.
 7. An injectionneedle according to claim 3, wherein when the injection needle pierces asilicone rubber sheet having a thickness of 0.5 mm at a penetrationspeed of 10 mm/min., an initial value of the load with respect to apenetration distance is 6 gf/mm or less.